Most television (TV) apparatus includes a front panel keyboard for a user to operate the television apparatus. A television apparatus normally includes a controller for receiving, detecting, identifying key activation signals from the front panel keyboard, and operating the television according to the function of the key being activated, for example, by pressing or touching. The front panel keyboard may include a top light or a backlight for lighting the keyboard when the television apparatus has been powered on. In addition, the front panel keyboard may have a power LED to indicate that the TV is “on”. The top light, backlight, or power LED is turned on normally by a signal, such as a voltage, sent by the controller to the top light, backlight or power LED. The term “television apparatus” as used herein includes TV receivers having a display screen (commonly called TV sets), TV receivers without a display screen such as VCRs, VCPs (videocassette players), set-top boxes (such as cable boxes and satellite receivers), and Videodisk players.
In assembling a television apparatus, the front panel keyboard normally is one of the last few tasks to be installed. However, there are generally two different types of front panel keyboard to be supported: one with negative operational logic and the other with positive operational logic. In a keyboard with negative operation logic, the controller should provide a keyboard operational voltage to the keyboard. This type of keyboard normally uses momentary contact switches. By contrast, in a keyboard with positive operational logic, the keyboard provides its own keyboard operational voltage and the controller does not have to provide one for the keyboard. In general, front panel keyboards with positive operational logic have pull-down resistors on keyboard sense lines to set a logic zero condition on the keyboard inputs until a logic one is provided by a contact closure on the keyboard. A keyboard employing positive logic may have touch buttons, which use a capacitance change near a button indicating that the button has been pressed (activated).
In order to handle these two different types of keyboard, one may use a different television controller for each type of the front panel keyboard. However, the approach would significantly increase the cost of a television. Therefore, there is a need to design a television controller and keyboards, such that the television controller can be used with both types of keyboards.